An anisotropic conductive adhesive film, its preparation method and application

Abstract

This invention discloses an anisotropic conductive film, its preparation method, and its application. The preparation method includes the following steps: polyethylene glycol diacrylate, N,N'-dimethylethylenediamine, and pentaerythritol tetrakis(3-mercaptopropionic acid) ester are reacted to synthesize component A; silver nanosheets are then dispersed in polyethylene glycol diacrylate to obtain component B; components A and B are mixed with an organic solvent and coated into a liquid film; the substrate temperature and surface airflow are controlled to allow the solvent to evaporate before curing, thus obtaining the anisotropic conductive film. The anisotropic conductive film provided by this invention uses a hexamethylenetetramine polymer with self-catalytic function as a matrix, and silver nanosheets are oriented and aggregated along the Z-axis to form a continuous conductive path. It possesses high mechanical bonding strength, stable anisotropic conductivity, and excellent flexibility, making it suitable for the connection requirements of flexible hybrid electronic devices.

Description

Technical Field

[0001] This invention relates to the field of conductive adhesive film technology, specifically to an anisotropic conductive adhesive film, its preparation method, and its application. Background Technology

[0002] In recent years, flexible electronic devices have shown broad application prospects in fields such as medical and health monitoring, wearable devices, flexible displays, and intelligent sensing due to their excellent mechanical flexibility, design flexibility, and good adaptability to irregular surfaces (such as human skin and curved substrates). To achieve complex data processing, multifunctional integration, and high-performance output, the core architecture of existing flexible electronic devices mostly adopts a hybrid integration mode of flexible stretchable units and rigid functional units. That is, by combining flexible substrates and flexible circuits with rigid electronic components such as traditional silicon-based chips and printed circuit boards (PCBs), flexible hybrid electronic devices are constructed. This architecture leverages the adaptability advantages of flexible units while utilizing the high-performance computing and signal processing capabilities of rigid units.

[0003] However, in the integration of flexible hybrid electronic devices, reliable connection of the "soft-hard" interface has always been a key technical bottleneck restricting its industrial application. Rigid electronic components and flexible substrates differ by several orders of magnitude in mechanical properties such as elastic modulus and coefficient of thermal expansion. When the device is subjected to external forces such as tension and bending, stress is easily concentrated at the interface, leading to cracks, peeling, or even breakage of the connection layer, which seriously affects the long-term stability of the device. At the same time, the chemical properties of the two are significantly different, and traditional connection methods are difficult to form a stable interface bond. The connection can only be maintained by physical adsorption or weak mechanical interlocking. Under long-term use or environmental changes, interface peeling is prone to occur, causing the conductive path to be interrupted. Regarding conductive connection performance and process adaptability, existing technologies also suffer from the following problems: While metal welding can achieve high conductivity and high strength connections, the high-temperature process can cause irreversible damage to the heat-sensitive flexible substrate; traditional anisotropic conductive films (ACFs) require high-temperature and high-pressure conditions to achieve effective contact of conductive particles, which leads to substrate damage and complex processes; conventional conductive adhesives suffer from defects such as uneven dispersion of conductive particles, poor anisotropic conductivity, and high contact resistance, making it difficult to meet the connection requirements of high-precision flexible electronic devices. In addition, the preparation of some existing anisotropic conductive materials requires external magnetic fields, electric fields, and other auxiliary means to achieve the directional alignment of conductive particles. This not only requires expensive specialized equipment but also imposes strict limitations on the morphology, size, and substrate material of the conductive particles, resulting in high preparation costs, complex processes, and narrow applicability, making it difficult to adapt to diverse flexible hybrid electronic device assembly scenarios.

[0004] Therefore, developing a connection material and preparation method that combines high mechanical bonding strength, stable anisotropic conductivity, mild processing conditions, and wide applicability is of great significance for solving the "soft-hard" interface connection problem of flexible hybrid electronic devices and promoting the industrialization of flexible electronics technology. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of poor mechanical compatibility, low interface bonding strength, contradiction between conductivity and process adaptability, unstable connection, complex process, high preparation cost and insufficient versatility in the "soft-hard" interface connection of flexible hybrid electronic devices. The invention provides an anisotropic conductive film, its preparation method and application. The anisotropic conductive film has both high mechanical bonding strength and stable anisotropic conductivity, and the preparation process is mild and widely applicable.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution:

[0007] The first aspect of this invention provides a method for preparing anisotropic conductive adhesive film, comprising the following steps:

[0008] (1) Polyethylene glycol diacrylate and N,N'-dimethylethylenediamine were reacted in an organic solvent. After the reaction was completed, pentaerythritol tetrakis(3-mercaptopropionic acid) was added to continue the reaction. After the reaction was completed, component A was obtained.

[0009] (2) Silver nanosheets were dispersed in polyethylene glycol diacrylate to obtain component B;

[0010] (3) Mix component A obtained in step (1) and component B obtained in step (2) with an organic solvent to obtain a conductive film precursor solution; the organic solvent is selected from one or more of acetone, ethyl acetate and tetrahydrofuran (THF);

[0011] (4) The conductive film precursor solution obtained in step (3) is coated on the substrate surface to form a liquid film. The substrate temperature is controlled at 30-35 ℃ and the gas flow rate on the liquid film surface is 0.5-2.0 m / s. After the solvent evaporates, the film is cured to obtain the anisotropic conductive film.

[0012] This invention first involves an addition reaction between the double bond of polyethylene glycol diacrylate and the secondary amine of N,N'-dimethylethylenediamine to generate a diene compound with a tertiary amine side chain (catalytic base segment). This diene compound then undergoes a mercapto-ene click reaction with pentaerythritol tetrakis(3-mercaptopropionic acid) to form a cross-linked polymer matrix rich in mercapto groups (i.e., a hexamercaptopolymer matrix material with autocatalytic function), which serves as component A. Simultaneously, polyethylene glycol diacrylate is mixed with silver nanosheets to obtain conductive reinforcing component B. Components A and B were mixed with an organic solvent to prepare a conductive film precursor solution. After the solution was coated onto the substrate surface to form a liquid film, the temperature of the substrate and the gas flow rate on the surface of the liquid film were adjusted to create a significant difference in evaporation rate between the surface and the bottom of the liquid film, thereby constructing a surface tension gradient. This gradient drives the liquid to form Marangoni convection vortices perpendicular to the substrate. Silver nanosheets are pushed towards the boundary or center of the vortex cells under convection, forming a continuous conductive path along the thickness direction of the liquid film (Z-axis direction). At the same time, the interaction between the polythiol molecules and the surface of the silver nanosheets (coordination and van der Waals forces) further promotes the uniform dispersion and aggregation of conductive particles, ensuring the stability of anisotropic conductivity. After the solvent evaporates, the film is cured at room temperature, finally forming a conductive film with anisotropic conductivity in the Z-axis direction.

[0013] Further, in step (1), the mass ratio of polyethylene glycol diacrylate, N,N'-dimethylethylenediamine and pentaerythritol tetrakis(3-mercaptopropionic acid) is 10:(1-3):(8-15), preferably 10:(1.2-1.5):(8-10).

[0014] Further, in step (1), the organic solvent is tetrahydrofuran.

[0015] Further, in step (1), the number average molecular weight (Mn) of the polyethylene glycol diacrylate is 200-300, preferably 250.

[0016] Further, in step (1), the reaction temperature of the polyethylene glycol diacrylate with N,N'-dimethylethylenediamine is 30-45 °C and the time is 10-14 h.

[0017] Furthermore, in step (1), the reaction is continued at a temperature of 30-45°C for 10-14 h after the addition of pentaerythritol tetrakis(3-mercaptopropionic acid) ester.

[0018] Furthermore, in step (1), a purification step is also included after the reaction is completed.

[0019] Further, in step (1), the purification is carried out by column chromatography, and the eluent is a mixture of dichloromethane and methanol in a volume ratio of 9:1.

[0020] Furthermore, in step (2), the diameter of the silver nanosheets is 1-5 μm.

[0021] Further, in step (2), the mass ratio of polyethylene glycol diacrylate to silver nanosheets is 10:(1-6).

[0022] Further, in step (3), the mass ratio of component A, component B and organic solvent is 10:(1-6):(10-20).

[0023] Furthermore, in step (3), the mixing adopts a vortex oscillation method, and the mixing time is 30-180 s.

[0024] Furthermore, in step (4), the coating is applied by a scraping method, with a scraper height of 50-100 μm.

[0025] Furthermore, the scraper is made of stainless steel.

[0026] Further, in step (4), the substrate is a polyethylene terephthalate (PET) substrate, a polyimide (PI) substrate, a polydimethylsiloxane (PDMS) substrate, or a thermoplastic elastomer substrate.

[0027] Furthermore, in step (4), the thickness of the anisotropic conductive film is 5-10 μm.

[0028] The second aspect of the present invention provides an anisotropic conductive film prepared by the preparation method described in the first aspect.

[0029] The anisotropic conductive film provided by this invention uses a hexathyl mercapto polymer with self-catalytic function as a matrix, and silver nanosheets are oriented and aggregated along the Z-axis to form a continuous conductive path. It has high mechanical bonding strength, stable anisotropic conductivity and excellent flexibility, and can be adapted to the connection requirements of flexible hybrid electronic devices.

[0030] A third aspect of the present invention provides the application of the anisotropic conductive adhesive film described in the second aspect in the assembly of flexible hybrid electronic devices.

[0031] Furthermore, when the anisotropic conductive film provided by this invention is used for connecting flexible hybrid electronic devices, a silane coupling agent is used to modify the surface of the device to be connected. This treatment introduces functional groups into the surface that can specifically react with the thiol groups in the conductive film. With the help of the molecular-level bonding bridge formed by this surface modification, the anisotropic conductive film can achieve strong bonding between various materials under low-pressure conditions, while efficiently constructing a vertical electrical path with stable conductivity and reliable long-term use.

[0032] Furthermore, the silane coupling agent is 3-(acryloyloxy)propyltrimethoxysilane.

[0033] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0034] 1. This invention synthesizes a thiol polymer containing a self-catalytic base segment. The catalytic base segment serves as a built-in catalytic site, eliminating the need for additional catalysts and efficiently activating the Michael addition reaction between thiol groups and double bonds. This enables rapid room-temperature curing without the need for high-temperature hot-pressing, effectively avoiding damage to heat-sensitive flexible substrates caused by high temperatures, and is suitable for the assembly requirements of flexible hybrid electronic devices. Simultaneously, this invention utilizes the surface tension gradient generated by the evaporation of organic solvents to induce Marangoni convection circulation, synergistically promoting the interaction between multi-thiol molecules and silver nanosheets. This achieves Z-axis oriented alignment of silver nanosheets without the need for expensive external auxiliary equipment such as magnetic fields or electric fields. While reducing the amount of conductive filler used, this significantly lowers the preparation cost and process complexity, demonstrating potential for large-scale production.

[0035] 2. The abundant thiol groups in the anisotropic conductive adhesive film system provided by this invention can not only participate in the curing reaction of the adhesive film to ensure the stability of the adhesive film structure, but also chemically bond with the silane coupling agent pre-placed at the interface to be connected, significantly improving the bonding strength of the "soft-hard" interface. This solves the technical problems of poor adhesion and easy peeling of the "soft-hard" interface in flexible hybrid electronic devices, constructs a stable and reliable vertical electrical path, and can achieve strong bonding of various materials under low pressure.

[0036] 3. This invention employs a preparation method combining scraping and differential volatility control, which is flexible, simple, and highly repeatable. It is applicable to various substrate materials such as PET and PI, has a wide range of applications, and is conducive to large-scale production and promotion. The resulting anisotropic conductive film has both excellent flexibility and stable Z-axis anisotropic conductivity, low contact resistance, and can maintain stable conductivity and connection performance under deformation scenarios such as stretching and bending, fully meeting the long-term use requirements of flexible hybrid electronic devices. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the self-assembly mechanism induced by the Marangoni effect in this invention.

[0038] Figure 2 The diagram shows the process flow for preparing the anisotropic conductive film in Example 1, a physical image of component A, and an optical microscope image of the anisotropic conductive film.

[0039] Figure 3The images show cross-sectional scanning electron microscope (SEM) images of the anisotropic conductive films prepared in Examples 1-2, as well as energy dispersive X-ray spectra (EDS) of S and Ag elements; where (a) is Example 1 and (b) is Example 2.

[0040] Figure 4 The images show surface SEM images of the anisotropic conductive films prepared in Examples 2 and 9-13.

[0041] Figure 5 The anisotropic conductive films prepared in Examples 1-2 and the conductive films prepared in Comparative Examples 1-2 are viewed from the top under an optical microscope.

[0042] Figure 6 The images show a physical photograph of the high-resolution connection in Test Example 1 (left) and a photograph of the slit under an optical microscope (right).

[0043] Figure 7 This is a comparison of the changes in light intensity during bending after the flexible device circuit in Test Example 2 is connected by anisotropic conductive adhesive film.

[0044] Figure 8 The figure shows the test results of the anisotropic conductive film prepared in Example 1 under a constant current of 10mA.

[0045] Figure 9 The graphs show the shear strength test results of the anisotropic conductive films prepared in Examples 2 and 4-13; where (a) is the shear strength data graph of the anisotropic conductive films prepared in Examples 4-7, (b) is the shear strength data graph of the anisotropic conductive films prepared in Examples 2 and 8-13, and (c) is the curve of the shear strength of the anisotropic conductive films at 25 °C as a function of curing time. Detailed Implementation

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0047] This invention provides a method for preparing anisotropic conductive adhesive film, comprising the following steps:

[0048] (1) Polyethylene glycol diacrylate and N,N'-dimethylethylenediamine were reacted in an organic solvent. After the reaction was completed, pentaerythritol tetrakis(3-mercaptopropionic acid) was added to continue the reaction. After the reaction was completed, component A was obtained.

[0049] (2) Silver nanosheets were dispersed in polyethylene glycol diacrylate to obtain component B;

[0050] (3) Mix component A obtained in step (1) and component B obtained in step (2) with an organic solvent to obtain a conductive film precursor solution; the organic solvent is selected from one or more of acetone, ethyl acetate and tetrahydrofuran;

[0051] (4) The conductive film precursor solution obtained in step (3) is coated on the substrate surface to form a liquid film. The substrate temperature is controlled at 30-35 ℃, and the gas flow rate on the surface of the liquid film is controlled at 0.5-2.0 m / s. After the solvent evaporates, it is cured to form the anisotropic conductive film.

[0052] In a specific embodiment, the preparation method includes the following steps:

[0053] (1) Polyethylene glycol diacrylate was dissolved in tetrahydrofuran at room temperature (25±5 ℃) with stirring. Then, N,N'-dimethylethylenediamine was added in portions. The mass ratio of polyethylene glycol diacrylate, tetrahydrofuran and N,N'-dimethylethylenediamine was 10:11.1:(1.2-1.5). The temperature was raised to 30-45 ℃ and the reaction was stirred for 10-14 h to obtain a mixed polymer matrix material. Pentaerythritol tetrakis(3-mercaptopropionic acid) was dissolved in tetrahydrofuran and added to the mixed polymer matrix material. The mass ratio of the mixed polymer matrix material, pentaerythritol tetrakis(3-mercaptopropionic acid) to the newly added tetrahydrofuran was 11.2:(8-10):11. The temperature was maintained at 30-45 ℃ and the reaction was stirred for 10-14 h to obtain a mixed polymer matrix material. h; Purification was performed using a chromatography column, with a mixture of dichloromethane and methanol in a volume ratio of 9:1 as the eluent. The separated product was then evaporated by rotary evaporation to obtain component A.

[0054] (2) Polyethylene glycol diacrylate and silver nanosheets were added to a transparent sample bottle at a mass ratio of 10:(1-8), and mixed on a vortex mixer for 30-180 s to obtain component B;

[0055] (3) Add component A, component B and organic solvent to a transparent sample bottle at a mass ratio of 10:(1-6):15. After sealing the transparent sample bottle, mix it in a vortex mixer for 180 s to obtain a conductive film precursor solution.

[0056] (4) Take out the conductive film precursor solution using a pipette, and apply the conductive film precursor solution to the substrate surface by scraping to form a liquid film. Adjust the scraper height to 50-100 μm to control the thickness of the anisotropic conductive film. Control the substrate temperature to 30-35 ℃ and control the gas flow rate on the liquid film surface to 0.5-2.0 m / s. After the solvent evaporates, it solidifies to form the anisotropic conductive film.

[0057] The Marangoni convection-induced self-assembly mechanism is as follows: By heating the bottom of the liquid film and rapidly drying its surface, a significant temperature and concentration difference is created between the upper and lower surfaces, thereby constructing a gradient surface tension field. This surface tension gradient drives the liquid to flow from areas of lower surface tension to areas of higher surface tension, ultimately forming Marangoni convection vortices perpendicular to the substrate. Silver nanosheets are propelled to the boundaries or central regions of these vortices by this convection, accumulating and forming a uniform and ordered aggregate structure. This provides structural support for the anisotropic conductivity of the film along the Z-axis. A schematic diagram of the mechanism is shown below. Figure 1 As shown.

[0058] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0059] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0060] The polyethylene glycol diacrylate (PEGDA, average Mn 250), N,N'-dimethylethylenediamine and pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP) used in the following examples were purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd.; the silver nanosheets were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0061] Example 1

[0062] A method for preparing an anisotropic conductive adhesive film includes the following steps:

[0063] (1) PEGDA was dissolved in THF at 25 °C with stirring. Then, N,N'-dimethylethylenediamine was added in portions, and the mass ratio of PEGDA, THF and N,N'-dimethylethylenediamine was controlled at 10:11.1:1.2. The mixture was heated to 40 °C and stirred for 12 h. During this process, the secondary amine in N,N'-dimethylethylenediamine reacted with the double bond of PEGDA to generate an intermediate with a tertiary amine side chain. Then, PETMP was dissolved in THF and added to the above intermediate with a tertiary amine side chain. The mass ratio of the intermediate with a tertiary amine side chain, PETMP and the newly added THF was controlled at 11.2:9:11. The mixture was stirred at 40 °C for another 12 h. After the reaction, purification was performed using a chromatography column with a 9:1 volume ratio of dichloromethane to methanol as the eluent. The separated product was collected, and the solvent was removed by rotary evaporation to obtain a pure, pale yellow viscous liquid, which is component A. (See image below.) Figure 2 As shown in the upper right of the image.

[0064] (2) PEGDA and silver nanosheets with a diameter of 1-5 μm were added to a transparent sample bottle at a mass ratio of 10:5. The transparent sample bottle was placed on a vortex mixer and mixed at high speed for 180 s to make the silver nanosheets uniformly dispersed, thus obtaining component B.

[0065] (3) Add component A to a 4 mL transparent sample bottle, then add component B and acetone in sequence, and control the mass ratio of component A, component B and acetone to be 10:3:15; after sealing the transparent sample bottle, place it on a vortex shaker and mix for 30 s to obtain a uniformly dispersed conductive film precursor solution.

[0066] (4) Using a pipette, the above-mentioned conductive film precursor solution was drawn and dropped onto the surface of the PET substrate to be coated; a doctor blade was used for coating, and the height of the doctor blade was adjusted to 75 μm to control the coating thickness to 5 μm. The coated PET substrate was placed on a heating stage with the temperature set at 35 ℃, and a horizontal laminar flow with a flow rate of 1.0 m / s was applied above the liquid film; at 25 ℃, as acetone completely evaporated, the tertiary amine side chain in component A efficiently catalyzed its own mercapto group to undergo a Michael addition reaction with the double bond in component B. The PET substrate to be cured was left to stand at 25 ℃ for 10 min, and the film was completely cured to obtain an anisotropic conductive film with Z-axis conductivity. The preparation flowchart and optical microscope image are shown below. Figure 2 As shown.

[0067] Example 2

[0068] A method for preparing an anisotropic conductive adhesive film includes the following steps:

[0069] (1) PEGDA was dissolved in THF at 25 °C with stirring. Then, N,N'-dimethylethylenediamine was added in portions, and the mass ratio of PEGDA, THF and N,N'-dimethylethylenediamine was controlled at 10:11.1:1.5. The mixture was heated to 40 °C and stirred for 12 h. During this process, the secondary amine in N,N'-dimethylethylenediamine reacted with the double bond of PEGDA to generate an intermediate with a tertiary amine side chain. Then, PETMP was dissolved in THF and added to the above intermediate with a tertiary amine side chain. The mass ratio of the intermediate with a tertiary amine side chain, PETMP and the newly added THF was controlled at 11.2:9:11. The mixture was stirred at 40 °C for another 12 h. After the reaction was completed, the product was purified by chromatography using a 9:1 mixture of dichloromethane and methanol as the eluent. The separated product was collected and the solvent was removed by rotary evaporation to obtain a pure, pale yellow viscous liquid, which was component A.

[0070] (2) PEGDA and silver nanosheets with a diameter of 1-5 μm were added to a transparent sample bottle at a mass ratio of 10:5. The transparent sample bottle was placed on a vortex mixer and mixed at high speed for 180 s to make the silver nanosheets uniformly dispersed, thus obtaining component B.

[0071] (3) Add component A to a 4 mL transparent sample bottle, then add component B and acetone in sequence, and control the mass ratio of component A, component B and acetone to be 10:3:15; after sealing the transparent sample bottle, place it on a vortex shaker and mix for 30 s to obtain a uniformly dispersed conductive film precursor solution.

[0072] (4) Using a pipette, the above-mentioned conductive film precursor solution was drawn and dropped onto the surface of the PET substrate to be coated; a doctor blade was used for coating, and the height of the doctor blade was adjusted to 125 μm to control the coating thickness to 10 μm. The coated PET substrate was placed on a heating stage with the temperature set at 35 ℃, and a horizontal laminar flow with a flow rate of 1.0 m / s was applied above the liquid film; at 25 ℃, as acetone completely evaporated, the tertiary amine side chain in component A efficiently catalyzed its own mercapto group to undergo a Michael addition reaction with the double bond in component B. The PET substrate to be cured was left to stand at 25 ℃ for 10 min, and the film was completely cured to obtain an anisotropic conductive film with Z-axis conductivity.

[0073] Figure 3 The images show cross-sectional SEM images and EDS diagrams of S and Ag elements of the anisotropic conductive films prepared in Examples 1-2. Figure 3 As can be seen, silver nanosheets exhibit a discontinuous distribution in the anisotropic conductive film. This distribution pattern can effectively construct conductive pathways in the Z-axis direction while blocking lateral conductive paths, thereby endowing the film with excellent anisotropic conductivity.

[0074] The contact resistance of the anisotropic conductive films prepared in Examples 1-2 was quantitatively tested using the four-probe method. The results showed that the anisotropic conductive film prepared in Example 1 could achieve a contact resistance of 0.561 Ω·mm at a thickness of 5 μm. -2 Regarding the contact resistance, the anisotropic conductive film prepared in Example 2 achieves a resistance of 1.346 Ω·mm at a thickness of 10 μm. -2 The contact resistance is low, and this excellent conductivity can be achieved without relying on high-pressure bonding processes, only under mild room temperature and low-pressure conditions.

[0075] Example 3

[0076] A method for preparing an anisotropic conductive adhesive film includes the following steps:

[0077] (1) PEGDA was dissolved in THF at 25 °C with stirring. Then, N,N'-dimethylethylenediamine was added in portions, and the mass ratio of PEGDA, THF and N,N'-dimethylethylenediamine was controlled at 10:11.1:1.2. The mixture was heated to 40 °C and stirred for 12 h. During this process, the secondary amine in N,N'-dimethylethylenediamine reacted with the double bond of PEGDA to generate an intermediate with a tertiary amine side chain. Then, PETMP was dissolved in THF and added to the above intermediate with a tertiary amine side chain. The mass ratio of the intermediate with a tertiary amine side chain, PETMP and the newly added THF was controlled at 11.2:9:11. The mixture was stirred at 40 °C for another 12 h. After the reaction was completed, the product was purified by chromatography using a 9:1 mixture of dichloromethane and methanol as the eluent. The separated product was collected and the solvent was removed by rotary evaporation to obtain a pure, pale yellow viscous liquid, which was component A.

[0078] (2) PEGDA and silver nanosheets with a diameter of 1-5 μm were added to a transparent sample bottle at a mass ratio of 10:4. The transparent sample bottle was placed on a vortex mixer and mixed at high speed for 180 s to make the silver nanosheets uniformly dispersed, thus obtaining component B.

[0079] (3) Add component A to a 4 mL transparent sample bottle, then add component B and ethyl acetate in sequence, and control the mass ratio of component A, component B and ethyl acetate to be 10:2:15; after sealing the transparent sample bottle, place it on a vortex shaker and mix for 30s to obtain a uniformly dispersed conductive film precursor solution.

[0080] (4) Using a pipette, the above-mentioned conductive film precursor solution was drawn and dropped onto the surface of the PDMS substrate to be coated; a doctor blade was used for coating, and the height of the doctor blade was adjusted to 125 μm to control the coating thickness to 10 μm. The coated PDMS substrate was placed on a heating stage with the temperature set at 35 ℃, and a horizontal laminar flow with a flow rate of 1.0 m / s was applied above the liquid film; at 25 ℃, as the ethyl acetate completely evaporated, the tertiary amine side chain in component A efficiently catalyzed its own mercapto group to undergo a Michael addition reaction with the double bond in component B. The PDMS substrate to be cured was allowed to stand at 25 ℃ for 10 min, and the film was completely cured to obtain an anisotropic conductive film with Z-axis conductivity.

[0081] Example 4

[0082] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 1, except that in step (4), the PET substrate to be cured is left to stand at 60 °C for 30 min.

[0083] Example 5

[0084] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 1, except that in step (4), the PET substrate to be cured is left to stand at 100 °C for 2 min.

[0085] Example 6

[0086] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 2, except that in step (4), the PET substrate to be cured is left to stand at 60 °C for 30 min.

[0087] Example 7

[0088] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 2, except that in step (4), the PET substrate to be cured is left to stand at 100 °C for 2 min.

[0089] Example 8

[0090] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 1, except that in step (2), the mass ratio of PEGDA to silver nanosheets is 10:3.

[0091] Example 9

[0092] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 2, except that in step (2), the mass ratio of PEGDA to silver nanosheets is 10:1.

[0093] Example 10

[0094] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 2, except that in step (2), the mass ratio of PEGDA to silver nanosheets is 10:2.

[0095] Example 11

[0096] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 2, except that in step (2), the mass ratio of PEGDA to silver nanosheets is 10:3.

[0097] Example 12

[0098] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 2, except that in step (2), the mass ratio of PEGDA to silver nanosheets is 10:4.

[0099] Example 13

[0100] A method for preparing an anisotropic conductive adhesive film is basically the same as that in Example 2, except that in step (2), the mass ratio of PEGDA to silver nanosheets is 10:6.

[0101] Figure 4 The images show surface SEM images of the anisotropic conductive films prepared in Examples 2 and 9-13.

[0102] Comparative Example 1

[0103] A method for preparing a conductive adhesive film is basically the same as that in Example 1, except that in step (4), acetone is replaced with N,N-dimethylformamide (DMF).

[0104] Comparative Example 2

[0105] A method for preparing a conductive adhesive film is basically the same as that in Example 1, except that in step (4), the coated PET substrate is placed in an environment of 25 °C.

[0106] Comparative Example 3

[0107] A method for preparing a conductive adhesive film is basically the same as that in Example 1, except that in step (4), a horizontal laminar flow is not applied above the liquid film.

[0108] Figure 5 These are top views under an optical microscope of the anisotropic conductive films prepared in Examples 1-2 and the conductive films prepared in Comparative Examples 1-2. Figure 5As can be seen, in the conductive films prepared in Comparative Examples 1-2, the silver nanosheets are randomly dispersed, and the Z-axis conductivity of the conductive films is extremely poor. The conductive film prepared in Comparative Example 3 also exhibits poor Z-axis conductivity. These results demonstrate that the Marangoni convection constructed by controlling the solvent type, substrate temperature, and airflow on the liquid film surface is the key factor driving the directional alignment of silver nanosheets and endowing the films with excellent Z-axis anisotropic conductivity.

[0109] Test Example 1

[0110] A gold (Au) layer was deposited on the surface of a flexible PET film using a vacuum evaporation process, and a patterned conductive circuit (Au@PET circuit) with a slit width of only 23.19 μm was fabricated using a masking process. Subsequently, the surfaces of the Au@PET circuit and the 0805 LED chip to be connected were modified with 3-(acryloyloxy)propyltrimethoxysilane. An anisotropic conductive film was then prepared using the method of Example 1 of this invention. Using this conductive film as the connection medium, the surface-modified LED chip was placed above the circuit slit, and slight pressure was applied. Curing was completed at room temperature (25 °C), thus achieving the connection between the Au@PET circuit and the LED chip. After applying a 3 V voltage to both ends of the circuit, the LED chip successfully lit up. Figure 6 As shown. This result demonstrates that the anisotropic conductive film of the present invention can construct a stable longitudinal conductive path and achieve excellent anisotropic electrical connection effect in high-resolution circuit connection scenarios of 23.19 μm.

[0111] Test Example 2

[0112] A silver (Ag) layer was deposited on the surface of a flexible PET film using a vacuum evaporation process, and a patterned conductive circuit with a slit width of only 50 μm (i.e., Ag@PET circuit) was prepared using a masking process. Subsequently, the surfaces of the Ag@PET circuit and the 0805 LED chip to be connected were modified with 3-(acryloyloxy)propyltrimethoxysilane. An anisotropic conductive film was then prepared using the method of Example 2 of this invention. Using this conductive film as the connection medium, the surface-modified LED chip was placed above the circuit slit, and slight pressure was applied. Curing was completed at room temperature (25 °C) to achieve the connection between the Ag@PET circuit and the LED chip. After applying a 3 V voltage to both ends of the circuit, the flexible device was subjected to 500 bending tests. Figure 7 As shown, the results indicate that the light intensity of the LED chip remained almost unchanged, demonstrating that the anisotropic conductive film of the present invention can not only achieve stable anisotropic electrical connections at a high resolution of 50 μm, but also possesses excellent mechanical flexibility and connection reliability, and can withstand repeated bending while maintaining stable conductivity.

[0113] Test Example 3

[0114] A vacuum evaporation process was used to deposit gold (Au) electrodes on the surface of a flexible PET film. Two sets of symmetrically patterned conductive lines (Au@PET circuits) were then fabricated using a masking process, consisting of a bottom circuit and a top circuit. Each circuit contains three independent Au electrodes (200 μm wide), physically and electrically isolated from each other by 200 μm wide PET insulating slits without Au deposition. The conductive areas to be connected in both the bottom and top circuits were modified with 3-(acryloyloxy)propyltrimethoxysilane. The surface-modified conductive areas of the bottom and top circuits were then stacked face-to-face. An anisotropic conductive film was prepared using the method described in Example 1 of this invention. This conductive film served as the intermediate connecting medium to achieve vertical connections between the circuits. The gold area represents the Au electrodes, the gray / dark gray area represents the PET insulating surface without Au deposition, and the purple area represents the anisotropic conductive film used for connection. Anisotropic conductivity performance tests were conducted, and the results are shown below. Figure 8 As shown.

[0115] Under a constant current excitation of 10mA, the voltage-time characteristic curves of a single electrode path (L1-R1) and a path across the electrode gap (L1-R2) show the following: The red curve (L1-R1) represents the longitudinal (Z-axis) conductivity along the same Au electrode path. At the instant the current is applied, the voltage rises rapidly and remains stable at approximately 0.25V, indicating stable conduction and constant resistance in the longitudinal conductive path, demonstrating the excellent conductivity of the conductive film in the vertical direction. The purple curve (L1-R2) represents the lateral insulation performance across the gap between adjacent Au electrodes. Under the same current excitation, its voltage response remains close to 0V, and no effective lateral current path is detected, indicating good electrical isolation between adjacent electrodes. These results fully demonstrate that the anisotropic conductive film of this invention possesses significant anisotropic conductivity characteristics: it can construct a stable conductive path in the Z-axis direction perpendicular to the substrate and maintain excellent insulation performance in the horizontal direction, effectively avoiding signal crosstalk between adjacent electrodes and meeting the connection requirements of high-resolution flexible circuits.

[0116] Test Example 4

[0117] The anisotropic conductive films prepared in Examples 2 and 4-13 were subjected to shear strength testing and room temperature curing kinetic analysis. The shear strength testing method was as follows: a universal testing machine was used, with PET substrate as the test carrier, and the sample was prepared with an overlap area of ​​1 cm × 1 cm. The shear strength was calculated by the formula τ=F / S, where τ is the shear strength, F is the test load, and S is the overlap area.

[0118] Test results are as follows Figure 9 As shown, (a) the shear strength of the anisotropic conductive film at different temperatures and curing times was compared. The results showed that high-temperature curing at 100 °C enabled the conductive film to achieve a shear strength equivalent to that of curing at 60 °C for 30 min within 2 min; (b) the effects of different silver nanosheet ratios and film thickness on shear strength were investigated, indicating that the interfacial bonding of the conductive film mainly depends on the surface-to-interfacial chemical reaction between the substrate and the matrix, proving the mechanical stability of the preparation method under different process parameters; by changing the curing time of the anisotropic conductive film prepared in Example 2, (c) the curve of the shear strength of the anisotropic conductive film at 25 °C versus curing time was shown. It can be seen that the film can achieve a stable shear strength of about 1.0 MPa within 12 min, verifying the efficient curing ability of the self-catalytic system at room temperature without additional heating or pressurization.

[0119] In summary, this invention, leveraging the Marangoni effect-driven self-assembly mechanism, successfully overcomes the technical dependence of traditional anisotropic conductive films on external auxiliary fields such as magnetic and electric fields, achieving the directional arrangement of silver nanosheets along the Z-axis, thereby endowing the conductive film with excellent anisotropic conductivity. Simultaneously, based on an alkaline self-catalytic system, the conductive film can rapidly cure at room temperature (25 °C) in just about 10 minutes, effectively avoiding damage to heat-sensitive flexible substrates caused by high-temperature processes. Furthermore, the conductive film exhibits excellent electrical stability and mechanical reliability in 50 μm high-resolution circuit connection scenarios and 500 bending cycle tests, providing a novel technical solution for the low-cost, high-efficiency, large-scale assembly of flexible hybrid electronic devices.

[0120] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an anisotropic conductive adhesive film, characterized in that, Includes the following steps: (1) Polyethylene glycol diacrylate and N,N'-dimethylethylenediamine are reacted in tetrahydrofuran. After the reaction is completed, pentaerythritol tetrakis(3-mercaptopropionic acid) is added to continue the reaction. After the reaction is completed, component A is obtained. The mass ratio of polyethylene glycol diacrylate, N,N'-dimethylethylenediamine and pentaerythritol tetrakis(3-mercaptopropionic acid) is 10:(1-3):(8-15). (2) Disperse silver nanosheets in polyethylene glycol diacrylate to obtain component B; the mass ratio of polyethylene glycol diacrylate to silver nanosheets is 10:(1-6); (3) Mix component A obtained in step (1) and component B obtained in step (2) with an organic solvent to obtain a conductive film precursor solution; the organic solvent is acetone or ethyl acetate; the mass ratio of component A, component B and organic solvent is 10:(1-6):(10-20); (4) The conductive film precursor solution obtained in step (3) is coated on the substrate surface to form a liquid film. The substrate temperature is controlled at 30-35 ℃ and the gas flow rate on the liquid film surface is 0.5-2.0 m / s. After the solvent evaporates, the film is cured to obtain the anisotropic conductive film.

2. The preparation method according to claim 1, characterized in that, In step (1), the reaction temperature of polyethylene glycol diacrylate with N,N'-dimethylethylenediamine is 30-45 °C and the time is 10-14 h; the reaction temperature of pentaerythritol tetrakis(3-mercaptopropionic acid) is 30-45 °C and the time is 10-14 h.

3. The preparation method according to claim 1, characterized in that, In step (2), the diameter of the silver nanosheets is 1-5 μm.

4. The preparation method according to claim 1, characterized in that, In step (4), the substrate is a polyethylene terephthalate substrate, a polyimide substrate, a polydimethylsiloxane substrate, or a thermoplastic elastomer substrate.

5. The preparation method according to claim 1, characterized in that, In step (4), the thickness of the anisotropic conductive film is 5-10 μm.

6. An anisotropic conductive film prepared by the preparation method according to any one of claims 1-5.

7. The application of the anisotropic conductive adhesive film according to claim 6 in the assembly of flexible hybrid electronic devices.

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